Continuous haemodialysis and continuous haemofiltration are efficient and safe techniques for the treatment of acute renal failure. Theoretical advantages are improved haemodynamic stability and easier fluid removal. All 15 available studies comparing intermittent (522 patients) with continuous (651 patients) renal replacement therapy have been reviewed. From these studies it cannot be established, whether the use of a continuous instead of an intermittent treatment modality improves the outcome in patients with acute renal failure. Reviewing all 67 published studies dealing with continuous renal replacement therapy revealed a trend to a decreasing mortality rate (P<0.08) over the last 11 years, whereas the mean age and the severity of illness of the patients, measured by the APACHE II score, did not change, In order to establish whether the quality of treatment has improved as a function of time, two quality factors (QF) were created, i.e. QF for age (mean age/mean mortality rate of the patients treated) and QF for severity of diseases (mean APACHE II/mean mortality rate). Both QF improved from 1984 until 1994, when analyzed for continuous (P<0.001) or intermittent (P<0.001) treatment modality. Thus the quality of treatment of patients with acute renal failure improved during the last decade. However, there is no evidence with respect to survival rate that a continuous renal replacement therapy is superior to an intermittent one.